Hst and transmission device

ABSTRACT

An HST of the present invention includes a main plate and a sub-plate supporting a center section, a pump-side swash plate holder and a motor-side swash plate holder by their inner surfaces facing each other. The main plate is provided with an extended region that extends farther outward in a planar direction of the main plate than an installation space of the center section, the pump-side swash plate holder and the motor-side swash plate holder and than the sub-plate as viewed along a direction in which the main plate and the sub-plate face each other.

FIELD OF THE INVENTION

The present invention relates to an HST (Hydrostatic Transmission) including a hydraulic pump and a hydraulic motor that are fluidly connected to each other, and a transmission including the HST.

BACKGROUND ART

An HST capable of speed-change a rotational power in a stepless manner is preferably used as a part or a whole of a travel system transmission provided in a work vehicle such as a combine harvester and a tractor.

The following patent literature 1 discloses a transmission that shifts and transmits a rotational power from an engine arranged in front to a rear wheel that serves as a drive wheel, and that has a casing provided with an opening that opens upward and an HST housed in the casing, wherein all components of the HST are supported by a cover that closes the opening.

The transmission described in the patent literature 1 is useful in that the HST can be removed by removing the cover from the casing while the casing is mounted on a vehicle.

However, in the configuration described in the patent literature 1, all components of the HST are supported by the cover in a cantilevered state, causing a problem that support stability is lacking.

PRIOR ART DOCUMENT Patent Literature

-   Patent Literature 1: Japanese Patent Application Laid-Open No. Showa     53 (1978)-016223

SUMMARY OF THE INVENTION

The present invention has been made in view of the conventional technology, and it is a first object to provide an HST that can be integrally attached to and detached from a transmission case in a work vehicle without disassembling components of the work vehicle, while stabilizing a supporting state of the components including a center section, a pump-side swash plate holder, and a motor-side swash plate holder.

In addition, it is a second object of the present invention to provide a transmission that shifts a rotational power operatively input from a drive source, and, with the installation state of the transmission case maintained, that can be attached to and detached from the transmission case without disassembling the HST, while stabilizing the support of the HST components including the center section, the pump-side swash plate holder, and the motor-side swash plate holder.

In order to achieve the first object, the present invention provides an HST including a pump shaft, a pump main body supported by the pump shaft in a manner relatively non-rotatable around an axial line with respect to the pump shaft, a pump-side swash plate defining a capacity of the pump main body, a pump-side swash plate holder supporting a rear surface of the pump-side swash plate, a motor shaft, a motor main body supported by the motor shaft in a manner relatively non-rotatable around an axial line with respect to the motor shaft, a motor-side swash plate defining a capacity of the motor main body, a motor-side swash plate holder supporting a rear surface of the motor-side swash plate, a center section on which the pump main body and the motor main body directly or indirectly abut in a slidable manner around the respective axial lines and which is formed with oil paths fluidly connecting the pump main body and the motor main body, and a main plate and a sub-plate hold or support the center section, the pump-side swash plate holder and the motor-side swash plate holder in a sandwiched manner by inner surfaces of the main plate and the sub-plate that face each other, wherein the main plate is provided with an extended region that extends farther outward in a planar direction of the main plate than an installation space of the center section, the pump-side swash plate holder and the motor-side swash plate holder, and than the sub-plate as viewed along a direction in which the main plate and the sub-plate face each other.

The HST according to the present invention makes it possible to be attached to and detached from a transmission case in a work vehicle without being disassembled while stabilizing the support of components including the center section, the pump-side swash plate holder and the motor-side swash plate holder.

In a first example of a first embodiment, the HST is of an in-line type in which the pump main body and the motor main body that are respectively arranged on one side and the other side in a thickness direction of the center section while being coaxially with each other.

In a second example of the first embodiment, the pump main body is arranged on one side in the thickness direction of the center section, and the motor main body is arranged on the other side in the thickness direction of the center section with a shaft line of the motor main body being parallel to and displaced from a shaft line of the pump main body.

In a preferable configuration of the first embodiment, an inner surface of at least one of the main plate and the sub-plate is provided with a pump-side concave portion into which the pump-side swash plate holder is engaged and a motor-side concave portion into which the motor-side swash plate holder is engaged.

The pump-side concave portion and the motor-side concave portion are so configured as to prevent the pump-side swash plate holder and the motor-side swash plate holder from moving in a direction away from or a direction close to the center section with respect to the thickness direction of the center section.

In a preferable configuration of the first embodiment, an inner surface of at least one of the main plate and the sub-plate is provided with a center section-directed concave portion in which the center section is engaged in a manner to be immovable in the thickness direction of the center section.

The HST according to a second embodiment is of a parallel type in which the pump main body and the motor main body are arranged on one side in a thickness direction of the center section with their axial lines being parallel to each other.

In a preferable configuration of the second embodiment, the HST may include a common swash plate holder integrally having the pump-side swash plate holder and the motor-side swash plate holder.

In a more preferable configuration, an inner surface of at least one of the main plate and the sub-plate is provided with an engagement concave portion into which at least one of the common swash plate and the center section so that an HST preassembly in which the center section, the pump shaft, the pump main body, the pump-side swash plate, the motor shaft, the motor main body, the motor-side swash plate and the common swash plate holder are assembled is prevented from moving in the axial line direction of the pump shaft.

In any one of the above various configurations, at least one of the pump-side swash plate holder and the motor-side swash plate holder may support the rear surface of the corresponding swash plate in such a manner that the corresponding swash plate is swingable around a swing axial line.

In this case, the main plate is preferably provided with a hydraulic servo mechanism that swings a movable swash plate, which is supported in a swingable manner around the corresponding swing axial line among the pump-side swash plate and the motor-side swash plate, around the corresponding swing axial line.

For example, the hydraulic servo mechanism may include a pushing piston that is housed in the main plate in a manner to be reciprocally movable in a pushing direction and is operatively connected to the movable swash plate via a connecting rod so that the movable swash plate swings around the swing axial line in accordance with a movement of the pushing piston along the pushing direction, first and second hydraulic oil chambers formed in the main plate in such a manner that pressure oil supplied into the first and second hydraulic oil chambers push the pushing piston to one side and the other side in the pushing direction, respectively, a switching spool that switches supply and discharge of pressure oil to and from the first and second hydraulic oil chambers in accordance with a position in a switching direction, an operating piston that is housed in the main plate in a manner to be reciprocally movable in an operating direction parallel to the switching direction and is operatively connected to the switching spool via a connection pin, first and second operation oil chambers formed in the main plate in such a manner that pressure oil supplied into the first and second operation oil chambers push the operating piston to one side and the other side in the operating direction, and an operating valve that switches supply and discharge of pressure oil to and from the first and second operation oil chambers.

In this case, the main plate is preferably provided with a manual operating mechanism capable of manually changing the position of the switching spool in the switching direction.

In order to achieve the second object, the present invention provides a transmission that speed-changes rotational power operatively input from a drive source, the transmission including a transmission case, an input-side transmission shaft that is operatively connected to the drive source and is supported by the transmission case in a rotatable manner around an axial line, an input-side transmission gear supported by the input-side transmission shaft in a manner relatively non-rotatable around an axial line with respect to the input-side transmission shaft within the transmission case, an output-side transmission shaft supported by the transmission case in a rotatable manner around an axial line, an output-side transmission gear supported by the output-side transmission shaft in a manner relatively non-rotatable manner around an axial line with respect to the output-side transmission shaft within the transmission case, and the HST.

According to the transmission of the present invention, it is possible to attach and detach the HST to and from the transmission case without disassembling the HST and with keeping an installation state of the transmission case while stabilizing the support of components including the center section, the pump-side swash plate holder and the motor-side swash plate holder.

In the transmission according to the present invention, the HST includes a pump shaft, a pump main body supported by the pump shaft in a manner relatively non-rotatable around an axial line with respect to the pump shaft, a pump-side swash plate defining a capacity of the pump main body, a pump-side swash plate holder that supports a rear surface of the pump-side swash plate and is formed with a through hole through which the pump shaft is passed, a pump-side transmission gear supported by a portion of the pump shaft that extends from a portion passing through the pump-side swash plate holder in a direction away from the pump main body in such a manner that the pump-side transmission gear is relatively non-rotatable around the axial line with respect to the pump shaft, a motor shaft, a motor main body supported by the motor shaft in a manner relatively non-rotatable around an axial line with respect to the motor shaft, a motor side swash plate defining a capacity of the motor main body, a motor-side swash plate holder that supports a rear surface of the motor-side swash plate and is formed with a through hole through which the motor shaft is passed, a motor-side transmission gear supported by a portion of the motor shaft that extends from a portion passing through the motor-side swash plate holder in a direction away from the motor main body in such a manner that the motor-side transmission gear is relatively non-rotatable around the axial line with respect to the motor shaft, a center section that is formed with oil paths fluidly connecting the pump main body and the motor main body, and a main plate and a sub-plate hold or support the center section, the pump-side swash plate holder and the motor-side swash plate holder in a sandwiched manner by inner surfaces of the main plate and the sub-plate that face each other.

The transmission case has a peripheral wall and an opening formed in the peripheral wall. The opening is so sized as to allow, in an assembled state of the HST, insertion of components other than the main plate of the HST. The main plate is detachably connected to an outer surface of the peripheral wall of the transmission case so that the components of the HST other than the main plate is housed within the transmission case via the opening.

The pump-side transmission gear and the motor-side transmission gear is so configured as to mesh with the input-side transmission gear and the output-side transmission gear, respectively, in accordance with connection of the main plate to the outer surface of the peripheral wall of the transmission case.

In one embodiment of the transmission according to the present invention, the main plate is formed with a supply oil path having one end portion opened to an outer surface to form an inlet port for receiving charge oil of operation oil of the HST. The pump-side swash plate holder and the motor-side swash plate holder are formed with oil paths receiving a part of oil supplied into the supply oil path. The pump shaft is formed with an axial line hole receiving at least a part of oil introduced into the oil path of the pump-side swash plate holder, and the motor shaft is formed with an axial line hole receiving at least a part of oil introduced into the oil path of the motor-side swash plate holder.

The axial line hole of the pump shaft and the axial line hole of the motor shaft is so configured as to supply the introduced oil to a site to be lubricated.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a power transmission of a work vehicle to which a transmission including an HST according to a first embodiment of the present invention is applied.

FIG. 2 is an exploded perspective view of a transmission case and the HST in the transmission.

FIG. 3 is an exploded perspective view of the HST.

FIG. 4 is a transverse cross-sectional plan view of the HST.

FIG. 5 is a hydraulic circuit diagram of the HST.

FIG. 6 is a cross-sectional view along the line VI-VI in FIG. 4.

FIG. 7 is a cross-sectional view along the line VII-VII in FIG. 4.

FIG. 8 is a cross-sectional view along the lines VIII-VIII in FIG. 4.

FIG. 9 is a cross-sectional view along the line IX-IX in FIG. 4.

FIG. 10 is a cross-sectional view along the line X-X in FIG. 4.

FIG. 11 is a cross-sectional view along the line XI-XI in FIG. 4.

FIG. 12 is a front view of the HST in a state of being mounted on the transmission case, as viewed from the outside of the transmission case, and illustrates the part XII in FIG. 2 in cross section.

FIG. 13 is a cross-sectional view along the line XIII-XIII in FIG. 12.

FIG. 14 is a cross-sectional view along the line XIV-XIV in FIG. 4.

FIG. 15 is a schematic diagram of power transmission of a work vehicle to which another transmission including the HST is applied.

FIG. 16 is a vertical cross-sectional view of an HST according to a second embodiment of the present invention, and shows the vertical cross-sectional view corresponding to FIG. 6.

FIG. 17 is a cross-sectional view along the line XVII-XVII in FIG. 16.

FIG. 18 is a vertical cross-sectional view of an HST according to a third embodiment of the present invention, and shows the vertical cross-sectional view corresponding to FIGS. 6 and 16.

EMBODIMENT FOR CARRYING OUT THE INVENTION First Embodiment

One embodiment of an HST according to the present invention will be described below with reference to the accompanying drawings.

FIG. 1 illustrates a schematic diagram of a power transmission of a work vehicle 1 to which a transmission 10A provided with an HST 100A according to the present embodiment is applied.

FIG. 2 illustrates an exploded perspective view of a transmission case 20 and the HST 100A in the above transmission 10A.

Further, FIGS. 3 to 5 illustrate an exploded perspective view, a transverse cross-sectional plan view, and a hydraulic circuit diagram of the HST 100A, respectively.

As illustrated in FIGS. 3, 4 and the like, the HST 100A includes a pump shaft 110 that operatively inputs a rotational power from a drive source 5 (FIG. 1) provided in the work vehicle 1, a pump main body 115 that is relatively non-rotatably supported by the pump shaft 110, a pump-side swash plate 120 that defines a capacity of the pump main body 115, a pump-side swash plate holder 125A which supports a rear surface of the pump-side swash plate 120, a motor shaft 130, a motor main body 135 which is relatively non-rotatably supported by the motor shaft 130, a motor-side swash plate 140 which defines a capacity of the motor main body 135, a motor-side swash plate holder 145A which supports a rear surface of the motor-side swash plate 140, a center section 150A, a main plate 160A, and a sub-plate 170A.

The HST 100A according to the present embodiment is of an in-line type in which the pump main body 115 and the motor main body 135 are arranged on one side and the other side in the thickness direction of the center section 150A, respectively, while being coaxially with each other.

FIG. 6 illustrates a cross-sectional view along the line VI-VI in FIG. 4. As illustrated in FIGS. 4 and 6, the pump main body 115 has a pump-side cylinder block 116, and pump-side pistons 118 housed in the pump-side cylinder block 116 so as to be relatively non-rotatable around an axial line and to advance and retreat in an axial line direction with respect thereto.

The pump-side cylinder block 116 is relatively non-rotatably supported by the pump shaft 110 with a base end surface directly or indirectly contacting a first end surface on one side in the thickness direction of the center section 150A.

The pump-side swash plate 120 is engaged with tip end portions of the pump-side pistons 118 so as to define the advance or retreat amount of the pump-side pistons 118 per revolution around the axial line of the pump-side cylinder block 116, that is, the capacity of the pump main body 115.

In the present embodiment, the pump-side swash plate 120 is a movable swash plate that can swing around the swing axial line, and according to the swing position of the pump-side swash plate 120 around the swing axial line, the advance or retreat amount of the pump-side piston 118 changes thereby to change the capacity of the pump main body 115.

The pump-side swash plate holder 125A is arranged in a manner to support the rear surface of the pump-side swash plate 120 (a surface opposite in the axial line direction to the surface with which the pump-side piston 118 is engaged).

As described above, in the present embodiment, the pump-side swash plate 120 is a movable swash plate that can swing around the swing axial line.

Accordingly, as illustrated in FIG. 6, the pump-side swash plate holder 125A has a concave support surface along the swing path of the rear surface of the pump-side swash plate 120 which path is seen when the pump-side swash plate 120 is swung around the swing axial line.

With the base end and tip end portions thereof rotatably supported by the center section 150A and the pump-side swash plate holder 125A, respectively, the pump shaft 110 supports the pump main body 115 at a middle portion in a manner relatively non-rotatable around the axial line with respect to the pump shaft 110.

The pump-side swash plate 120 is provided with a through hole that allows the pump shaft 110 to pass through.

As illustrated in FIGS. 4 and 6, the motor main body 135 has a motor-side cylinder block 136 and motor-side pistons 138 housed in the motor-side cylinder block 136 so as to be relatively non-rotatable around an axial line and to advance and retreat in an axial line direction with respect thereto.

With the base end surface directly or indirectly contacting the second end surface on the other side in the thickness direction of the center section 150A, the motor-side cylinder block 136 is supported by the motor shaft 130, which is arranged coaxially with the pump shaft 110, in a manner relatively non-rotatable around the axial line with respect to the motor shaft 130.

The motor-side swash plate 140 is engaged with the tip end portions of the motor-side pistons 138 so as to define the advance or retreat amount of the motor-side pistons 138 per revolution around the axial line of the motor-side cylinder block 136, that is, the capacity of the motor main body 135.

In the present embodiment, the motor-side swash plate 140 is a fixed swash plate in which a swash angle relative to the motor shaft 130 is fixed so that the capacity of the motor main body 135 is fixed.

The motor-side swash plate holder 145A is arranged in a manner to support the rear surface of the motor-side swash plate 140 (a surface opposite in the axial line direction to the surface with which the motor-side piston 138 is engaged).

As described above, in the present embodiment, the motor-side swash plate 140 is the fixed swash plate.

Accordingly, as illustrated in FIG. 6, the motor-side swash plate holder 145A has a swash support surface for fixing the motor-side swash plate 140 at a predetermined swash angle.

The motor shaft 130 is arranged coaxially with the pump shaft 110. With the base end and the tip end portions thereof rotatably supported by the center section 150A and the motor-side swash plate holder 145A, respectively, the motor shaft 130 supports the motor main body 135 at the middle portion in a manner relatively non-rotatable manner around the axial line with respect to the motor shaft 130.

The motor-side swash plate 140 is provided with a through hole that allows the motor shaft 130 to pass through.

FIG. 7 illustrates a cross-sectional view along the line VII-VII in FIG. 4.

As illustrated in FIG. 4, FIG. 7, etc., a pair of HST operation oil paths 151 which fluidly connects the pump main body 115 and the motor main body 135 is formed in the center section 150A.

The main plate 160A and the sub-plate 170A are so configured as to hold or support the center section 150A, the pump-side swash plate holder 125A, and the motor-side swash plate holder 145A in a sandwiched manner by their inner surfaces facing each other.

That is, the main plate 160A, with the inner surface thereof in contact with the side surfaces of the center section 150A, the pump-side swash plate holder 125A, and the motor-side swash plate holder 145A on one side in the width direction orthogonal to the thickness direction (that is, the axial line direction of the pump shaft 110 and the motor shaft 130), is connected to the above members by fastening members 190 (see FIG. 3), such as a bolt.

With the center section 150A, the pump-side swash plate holder 125A, and the motor-side swash plate holder 145A arranged between the inner surface of the sub-plate 170A and the inner surface of the main plate 160A, the sub-plate 170A is arranged so as to face the main plate 160A. Further, the inner surface of the sub-plate 170A is brought into contact with the side surfaces of the center section 150A, the pump-side swash plate holder 125A, and the motor-side swash plate holder 145A on the other side in the width direction, and is connected to the above members by fastening members 191 (see FIG. 3), such as a bolt.

As illustrated in FIGS. 3, 4, 6, and 7, etc., when viewed along a direction in which the main plate 160A and the sub-plate 170A face each other (i.e., a direction orthogonal to plate surfaces of the main plate 160A and the sub-plate 170A), the main plate 160A is provided with an extended region 162 that extends farther outward in the planar direction than an installation space of the center section 150A, the pump-side swash plate holder 125A, and the motor-side swash plate holder 145A, and than the sub-plate 170A.

According to the HST 100A having such a configuration, since the center section 150A, the pump-side swash plate holder 125A, and the motor-side swash plate holder 145A are supported at both sides by the main plate 160A and the sub-plate 170A, the support of the components can be stabilized.

Further, in the transmission case 20 to which the HST 100A is mounted, providing an opening 22 (see FIG. 2) that is smaller than the extended region 162 of the main plate 160A and larger than the installation space of the center section 150A, the pump-side swash plate holder 125A, and the motor-side swash plate holder 145A, and than the sub-plate 170A makes it possible to attach or detach the HST 100A to or from the transmission case 20 without disassembling the HST 100A. Accordingly, the maintenance work and component replacement work of the HST 100A can be facilitated.

In detail, as illustrated in FIGS. 1 and 2, the transmission 10A is provided with the transmission case 20, an input-side transmission shaft 30 which is, in a state of being operatively connected to the drive source 5, supported by the transmission case 20 in a manner to rotate around an axial line, an input-side transmission gear 32 supported by the input-side transmission shaft 30 in a manner relatively non-rotatable around the axial line with respect to the input-side transmission shaft 30 within the transmission case 20, an output-side transmission shaft 35 supported by the transmission case 20 in a manner to rotate around an axial line, an output-side transmission gear 37 supported by the output-side transmission shaft 35 in a manner relatively non-rotatable manner around the axial line with respect to the output-side transmission shaft 35 within the transmission case 20, and the HST 100A. The input-side transmission gear 32 and the output-side transmission gear 37 are arranged axially spaced apart within a front half portion or a first half portion of the transmission case 20.

The HST 100A is so configured as to be detachably attached to the transmission case 20, and so configured that when the HST 100A is mounted on the transmission case 20, the pump shaft 110 is operatively connected to the input-side transmission shaft 30 and the motor shaft 130 is operatively connected to the output-side transmission shaft 35.

In detail, as illustrated in FIGS. 1 to 4 and the like, the HST 100A further has a pump-side transmission gear 112 supported by the pump shaft 110 in a manner relatively non-rotatable around the axial line with respect to the pump shaft 110 and a motor-side transmission gear 132 supported by the motor shaft 130 in a manner relatively non-rotatable around the axial line with respect to the motor shaft 130.

In the present embodiment, the pump-side transmission gear 112 is supported at a portion of the pump shaft 110 that extends from a portion passing through the pump-side swash plate holder 125A in a direction away from the pump main body 115, and the motor-side transmission gear 132 is supported at a portion of the motor shaft 130 that extends from a portion passing through the motor-side swash plate holder 145A in a direction away from the motor main body 135.

As illustrated in FIG. 2, the transmission case 20 has, in the first half portion thereof, a peripheral wall 21 and the opening 22 provided in the peripheral wall 21.

The opening 22 is so sized as to allow, in the assembled state of the HST 100A, insertion of components other than the main plate 160A in the HST 100A.

That is, the opening 22 is so configured as to be larger than the installation space of the center section 150A, the pump-side swash plate holder 125A, and the motor-side swash plate holder 145A, and than the sub-plate 170A, but smaller than the extended region 162 of the main plate 160A.

In the present embodiment, the opening 22 is provided at a side surface of the peripheral wall 21, the side surface being located on the side based on the state in which the transmission case 20 is mounted on the work vehicle 1.

Alternatively, it is also possible to provide the opening 22 at an upper surface or a lower surface of the peripheral wall 21.

As illustrated in FIGS. 2 and 3, fastening holes 163 through which fastening members such as a bolt can be inserted are formed at the extended region 162 of the main plate 160A.

The extended region 162 is brought in contact with an outer surface of the peripheral wall 21 of the transmission case 20 in a state in which the HST 100A's component other than the main plate 160A is housed within the transmission case 20 via the opening 22, and is detachably connected to the outer surface via fastening members such as a bolt to be inserted into the fastening hole 163.

Further, the pump-side transmission gear 112 and the motor-side transmission gear 132 are so arranged to respectively mesh with the input-side transmission gear 32 and the output-side transmission gear 37 in accordance with connection of the extended region 162 of the main plate 160A to the outer surface of the peripheral wall 21 of the transmission case 20.

As illustrated in FIGS. 3 and 4, in the present embodiment, the inner surfaces of the main plate 160A and the sub-plate 170A are provided with center section-directed concave portions 165 and 175 in which the center section 150A is engaged in a manner to be immovable in the thickness direction.

Providing such a configuration makes it possible to stabilize the support of the HST preassembly in which the center section 150A, the pump shaft 110, the pump main body 115, the pump-side swash plate 120, the pump-side swash plate holder 125A, the motor shaft 130, the motor main body 135, the motor-side swash plate 140, and the motor-side swash plate holder 145A are assembled.

In the present embodiment, the main plate 160A and the sub-plate 170A are formed with the center section-directed concave portions 165 and 175, respectively, but it is possible that only one of the main plate 160A and the sub-plate 170A is formed with the corresponding concave portion.

Further, as illustrated in FIGS. 3 and 4, in the present embodiment, the inner surfaces of the main plate 160A and the sub-plate 170A are provided with pump-side concave portions 166 and 176 into which the pump-side swash plate holder 125A is engaged, and motor-side concave portions 167 and 177 into which the motor-side swash plate holder 145A is engaged.

The pump-side concave portions 166, 176 and the motor-side concave portions 167, 177 are so configured as to prevent the pump-side swash plate holder 125A and the motor-side swash plate holder 145A from moving in a direction away from the center section 150A with respect to the thickness direction (axial line direction of the pump shaft 110 and the motor shaft 130).

As illustrated in FIG. 4, in the present embodiment, the pump-side concave portions 166 and 176 have step portions 166 a and 176 a that engage with end surfaces of the pump-side swash plate holder 125A on a far side from the center section 150A.

The motor-side concave portions 167 and 177 have step portions 167 a and 177 a that engage with end surfaces of the motor-side swash plate holder 145A on a far side from the center section 150A.

Providing such a configuration can further stabilize the support state of the HST preassembly.

In place of this configuration, the pump-side concave portions 166, 176 and the motor-side concave portions 167, 177 can be so configured as to prevent the pump-side swash plate holder 125A and the motor-side swash plate holder 145A from moving in a direction proximate to the center section 150A with respect to the thickness direction.

That is, the pump-side concave portions 166 and 176 can be so configured as to have step portions that engage with the end surfaces of the pump-side swash plate holder 125A on a near side to the center section 150A, and the motor-side concave portions 167 and 177 can be so configured as to have step portions that engage with the end surfaces of the motor-side swash plate holder 145A on a near side to the center section 150A.

In the present embodiment, as illustrated in FIG. 7, the center section-directed concave portions 165, 175 have step portions 165 a, 165 b, 175 a, 175 b that engage with the lower surface and upper surface of the center section 150A.

FIGS. 8 and 9 illustrate cross-sectional views along the lines VIII-VIII and IX-IX in FIG. 4, respectively.

As illustrated in FIG. 8, in the present embodiment, the pump-side concave portions 166 and 176 have step portions 166 b, 176 b, 166 c, and 176 c that engage with the lower surface and upper surface of the pump-side swash plate holder 125A.

Similarly, as illustrated in FIG. 9, the motor-side concave portions 167 and 177 have step portions 167 b, 177 b, 167 c, and 177 c that engage with the lower surface and upper surface of the motor-side swash plate holder 145A.

Such a configuration can further stabilize the support of the HST preassembly.

In the present embodiment, the center section-directed concave portions 165 and 175 have step portions 165 a and 175 a that engage with the lower surfaces of the center section 150A and step portions 165 b and 175 b that engage with the upper surfaces of the center section 150A, but alternatively, can be modified in such a way as to have only the step portion that engages with any one of the lower surface and the upper surface.

The pump-side concave portions 166 and 176 and the motor-side concave portions 167 and 177 have step portions 166 b, 176 b, 167 b, and 177 b that engage with the lower surfaces of the corresponding swash plate holder and step portions 166 c, 176 c, 167 c, and 177 c that engage with the upper surfaces of the corresponding swash plate holder, but alternatively, can be transformed in such a way as to have only the step portion that engages with any one of the lower surface and the upper surface.

In the present embodiment, although the pump-side concave portions 166 and 176 are provided in the main plate 160A and the sub-plate 170A respectively, and the motor-side concave portions 167 and 177 are provided in the main plate 160A and the sub-plate 170A respectively, it is also possible to provide the pump-side concave portion only in one of the main plate 160A and the sub-plate 170A, and/or to provide the motor-side concave portions only in one of the main plate 160A and the sub-plate 170A.

As illustrated in FIGS. 4 and 5, the above HST 100A according to the present embodiment further has a hydraulic servo mechanism 200 that generates a force for swinging a movable swash plate (the pump-side swash plate 120 in the present embodiment).

In the present embodiment, the hydraulic servo mechanism 200 is provided at the main plate 160A.

FIGS. 10 and 11 illustrate cross-sectional views along the lines X-X and XI-XI in FIG. 4, respectively.

As illustrated in FIGS. 4, 5, 10 and 11, the hydraulic servo mechanism 200 includes: a pushing piston 210 housed in the main plate 160A in a manner to be reciprocally movable in a direction (hereinafter, referred to as pushing direction) orthogonal to both the axial line of the hydraulic body (the pump main body 115 in the present embodiment) having the capacity varied by the movable swash plate (the pump-side swash plate 120 in the present embodiment) and the swing axial line, and is operatively connected to the movable swash plate via a connecting rod 205 so that the movable swash plate swings around the swing axial line by a movement along the pushing direction, first and second hydraulic oil chambers 215(1) and 215(2) formed in the main plate 160A in a manner that pressure oil supplied into the first and second hydraulic oil chambers push the pushing piston 210 to one side and the other side respectively in the pushing direction, respectively, a switching spool 220 that can selectively take: a first operation position where a hydraulic source is fluidly connected to the first hydraulic oil chamber 215(1) and the second hydraulic oil chamber 215(2) is drained thereby to supply the pressure oil from the hydraulic source to the first hydraulic oil chamber 215(1), a second operation position where the hydraulic source is fluidly connected to the second hydraulic oil chamber 215(2) and the first hydraulic oil chamber 215(1) is drained thereby to supply the pressure oil from the hydraulic source to the second hydraulic oil chamber 215(2), and a close position for closing the first hydraulic oil chamber 215(1) and the second hydraulic oil chamber 215(2), an operating piston 230 that is, in a state of being connected to the switching spool 220 via a connection pin 225, reciprocally housed in the main plate 160A, and can take: a first operation position, a hold position, and a second operation position for respectively positioning the switching spool 220 in the first operation position, the close position, and the second operation position, a first operation oil chamber 235(1) and a second operation oil chamber 235 (2) formed in the main plate 160A in a manner that the supplied pressure oil can push the operating piston 230 to the first operation position and the second operation position respectively, and an operating valve 250 that can selectively take: a first position where the hydraulic source is fluidly connected to the first operation oil chamber 235(1) and the second operation oil chamber 235(2) is drained thereby to supply the pressure oil from the hydraulic source to the first operation oil chamber 235(1) so as to position the operating piston 230 in the first operation position, a second position where the hydraulic source is fluidly connected to the second operation oil chamber 235(2) and the first operation oil chamber 235(1) is drained thereby to supply the pressure oil from the hydraulic source to the second operation oil chamber 235(2) so as to position the operating piston 230 in the second operation position, and a close position where the first operation oil chamber 235(1) and the second operation oil chamber 235(2) are closed thereby to position the operating piston 230 in the hold position.

In the present embodiment, the switching spool 220 is housed in an axial line hole formed in the pushing piston 210, and the direction in which the switching spool reciprocates (switch direction) and the pushing direction in which the pushing piston reciprocates are the same.

In the present embodiment, the operating valve 250 is a solenoid valve that is operated and controlled by a control device provided in the work vehicle 1.

As illustrated in FIG. 5 and FIG. 10, in the present embodiment, a first spring 240(1) for biasing the operating piston 230 toward the first operation position is arranged in the first operation oil chamber 235(1), and a second spring 240(2) for biasing the operating piston 230 toward the second operation position is arranged in the second operation oil chamber 235(2).

The first and second springs 240(1), 240(2) are set to exert a biasing force in a manner to position the operating piston 230 in the hold position, when the pressure oil fails to act on both of the first and second operation oil chambers 235(1), 235(2).

The HST 100A further has a manual operating mechanism 260 for manually moving the switching spool 220.

In detail, as illustrated in FIG. 4, the direction in which the operating piston 230 reciprocates (operation direction) and the direction in which the switching spool 220 reciprocates (switch direction) are parallel to each other, and the connection pin 225 has a base end portion engaged with the switching spool 220 and a tip end portion engaged with the operating piston 230 so that the switching spool 220 moves along the switch direction in accordance with the movement of the operating piston 230 in the operation direction.

In the present embodiment, the manual operating mechanism 260 is provided at the main plate 160A.

In detail, the manual operating mechanism 260 has an operation shaft 265 supported by the main plate 160A rotatably around an axial line in a state that it is parallel to the connection pin 225 and its tip end portion extends outward, and a connection arm 270 that has a base end portion connected to the operation shaft 265 in a manner to be relatively non-rotatable around an axial line with respect thereto and has a tip end portion connected to the connection pin 225.

Rotating the operation shaft 265 around the axial line by human operation moves the switching spool 220 in the switch direction via the connection arm 270 and the connection pin 225.

Providing the manual operating mechanism 260 can provide a mode in which the switching spool 220 is moved by the human operation on the operation shaft 265, in addition to the mode in which the switching spool 220 is moved by the action of the hydraulic pressure via the operating valve 250.

Accordingly, even if one of the control structure for electrically controlling the position of the operating valve 250 and the manual operating mechanism for manually controlling the position of the operating valve 250 should fail due to some trouble, the position of the operating piston 230 can be controlled by the other.

Next, the oil path in the above HST 100A will be described.

FIG. 12 is a front view of the HST 100A in a state of being mounted on the transmission case 20, as viewed from the outside of the transmission case 20. In FIG. 12, the part XII in FIG. 2 is illustrated in cross section.

FIG. 13 illustrates a cross-sectional view along the line XIII-XIII in FIG. 12.

Further, FIG. 14 illustrates a cross-sectional view along the line XIV-XIV in FIG. 4.

As illustrated in FIGS. 2, 5, and 13, the main plate 160A has a supply oil path 310 having one end portion opened to an outer surface to form an inlet port 310P, a charge relief valve 315 that sets the hydraulic pressure of the supply oil path 310, a lubrication oil path 320 that receives a relief oil of the charge relief valve 315, and a lubrication relief valve 325 that sets the oil pressure of the lubrication oil path 320.

As illustrated in FIG. 5, in the present embodiment, the pressure oil is supplied to the inlet port 310P via a piping 305 from an auxiliary pump 9 driven by the drive source of the work vehicle 1.

As illustrated in FIGS. 5 and 14, the supply oil path 310 has a downstream in the pressure oil flow direction that is branched into a charge supply oil path 311 and a servo supply oil path 312.

As illustrated in FIG. 7, the charge supply oil path 311 has a downstream side in the pressure oil flow direction opening on a contact surface with the center section 150A thereby to form a main plate side charge port 311P.

In the present embodiment, as described above, the center section-directed concave portion 165 is formed in the main plate 160A in which the center section 150A is engaged in a manner to be immovable in the thickness direction, and the main plate side charge port 311P is provided on the bottom surface of the center section-directed concave portion 165.

As illustrated in FIGS. 5 and 7, the center section 150A is formed with, in addition to the above pair of HST operation oil paths 151, a charge oil path 153 having one end portion opened to an outer surface to form a center section side charge port 153P.

The charge oil path 153 has a downstream side in the pressure oil flow direction branched into two directions that are respectively fluidly connected to the pair of HST operation oil paths 151 via check valves 154.

As illustrated in FIG. 5, in the present embodiment, the check valve 154 is provided with a high-pressure relief function, so that when one HST operation oil path 151 has an abnormally high pressure, the pressure oil in the one HST operation oil path 151 is relieved to the other HST operation oil path 151.

The servo supply oil path 312 is so configured as to supply the pressure oil to the operating valve 250 and the switching spool 220.

As illustrated in FIGS. 8 and 9, the transmission case 20 is capable of storing the oil in the first half portion, and an oil level OL of the transmission case 20 is set lower so as not to become a rotational resistance of the pump main body 115 and the motor main body 135 when the HST 100A is mounted on the transmission case 20. For this reason, as illustrated in FIG. 5 and the like, the lubrication oil path 320 has a pump-side lubrication oil path 321 and a motor-side lubrication oil path 322 so that forced lubrication is made for the HST 100A.

As illustrated in FIGS. 4, 5, and 8, etc., the pump-side lubrication oil path 321 is communicated to a predetermined lubrication site such as a bearing or a piston shoe via a lubrication oil path 126 formed in the pump-side swash plate holder 125A and an axial line hole 111 formed in the pump shaft 110.

As illustrated in FIGS. 4, 5, and 9, etc., the motor-side lubrication oil path 322 is communicated to a predetermined lubrication site such as a bearing or a piston shoe via a lubrication oil path 146 formed in the motor-side swash plate holder 145A and an axial line hole 131 formed in the motor shaft 130.

A reference numeral 330 in FIG. 7 is a pressure oil takeout oil path having one end portion connected to the HST operation oil path 151 and the other end portion opened on the outer surface of the main plate 160A thereby to form a takeout port for measuring the pressure in the HST operation oil path 151, and a reference numeral 332 in FIG. 12 is a plug which closes the takeout port.

Herein, the transmission 10A will be described.

As illustrated in FIG. 1, according to the present embodiment, the transmission 10A has a multi-step speed-change mechanism 40 that changes the rotational power of the output-side transmission shaft 35 in multiple steps, a differential mechanism 45 that differentially transmits the output of the multi-step speed-change mechanism 40 to a pair of left and right main drive axles 80, a traveling brake mechanism 50 for applying a braking force to the main drive axles 80, and a sub-drive wheel-directed power takeout mechanism 55 capable of outputting the output of the multi-step speed-change mechanism 40 to the sub-drive wheel.

The transmission 10A further has a PTO shaft 90 capable of outputting the rotational power toward external equipment such as work equipment, a PTO transmission shaft 92 operatively connected to the input-side transmission shaft 30, a PTO brake mechanism 94 and a PTO speed-change mechanism 96 interposed in the PTO transmission path from the input-side transmission shaft 30 to the PTO shaft 90.

Naturally, the HST 100A is applicable to another transmission 10B.

FIG. 15 illustrates a schematic diagram of power transmission of the work vehicle 1 to which the other transmission 10B provided with the above HST 100A is applied.

In the figure, the same reference numerals are attached to the same components as in the present embodiment.

The transmission 10B has a planetary gear mechanism 60, a front/rear switching mechanism 65, and a multi-step speed-change mechanism 70, in place of the multi-step speed-change mechanism 40.

The planetary gear mechanism 60 has three planetary elements including a sun gear 61, a planetary carrier 62 and an internal gear 63, and is so configured as to synthesize the rotational power of the HST 100A input via the output-side transmission shaft 35 and the rotational power of the drive source 5 input via the input-side transmission shaft 30, and to output the synthesized rotational power.

In the configuration illustrated in the figure, the rotational power of the HST 100A is input to the sun gear 61 via the output-side transmission shaft 35, the rotational power of the drive source 5 is input to the internal gear 63 via the input-side transmission shaft 30, and the synthesized rotational power is output from the planetary carrier 62.

Second Embodiment

Another embodiment of the HST according to the present invention will be described below with reference to the accompanying drawings.

FIG. 16 illustrates a vertical cross-sectional view of an HST 100B according to the present embodiment in a state of being mounted on the transmission case 20, as viewed from the inside of the transmission case 20.

FIG. 17 illustrates a cross-sectional view along the line XVII-XVII in FIG. 16.

In the figure, the same components as those in the first embodiment described above are designated by the same reference numerals and the description thereof will be omitted as appropriate.

The HST 100B according to the present embodiment differs from the HST 100A according to the first embodiment in that the HST 100B is of a parallel type in which the pump main body 115 and the motor main body 135 are arranged on one side in a thickness direction of the center section 150B in a state parallel to each other.

Specifically, the HST 100B includes: a center section 150B, a pump-side swash plate holder 125B, a motor-side swash plate holder 145B, a main plate 160B and a sub-plate 170B that hold or support the center section 150B, the pump-side swash plate holder 125B, and the motor-side swash plate holder 145B in a sandwiched manner in a state where both the pump-side swash plate holder 125B and the motor-side swash plate holder 145B are arranged on one side of the center section 150B in the thickness direction, the pump shaft 110 supported rotatably around an axial line by the center section 150B and the pump-side swash plate holder 125B, the pump main body 115 supported by the pump shaft 110 in a manner relatively non-rotatable with respect to the pump shaft 110, the pump-side swash plate 120 having the rear surface supported by the pump-side swash plate holder 125B, the motor shaft 130 that is, in a state of being parallel to the pump shaft 110, supported by the center section 150B and the motor-side swash plate holder 145B in a manner to be rotatable around the axial line, the motor main body 135 supported by the motor shaft 130 in a manner relatively non-rotatable with respect to the motor shaft 130, and the motor-side swash plate 140 having the rear surface supported by the motor-side swash plate holder 145B.

As illustrated in FIGS. 16 and 17, in the present embodiment, the pump-side swash plate holder 125B and the motor-side swash plate holder 145B are formed by a single common swash plate holder 180.

That is, the HST 100B is provided with the common swash plate holder 180 integrally having a portion acting as the pump-side swash plate holder 125B and a portion acting as the motor-side swash plate holder 145B, and the main plate and the sub-plate are so configured as to hold or support the center section and the common swash plate holder in a sandwiched manner.

Similar to the main plate 160A in the first embodiment, when viewed along the direction in which the main plate 160B and the sub-plate 170B face one another, the main plate 160B is provided with the extended region 162 that extends farther outward in the planar direction than the installation space of the center section 150B, the pump-side swash plate holder 125B, and the motor-side swash plate holder 145B (that is, the common swash plate holder 180), and than the sub-plate 170B.

The inner surfaces of the main plate 160B and the sub-plate 170B are provided with engagement concave portions into which the common swash plate holder 180 and the center section 150B are engaged in a manner to prevent the HST preassembly from moving in the axial line direction.

In the present embodiment, as illustrated in FIGS. 16 and 17, the inner surface of the main plate 160B is provided with a swash plate holder-directed concave portion 350 forming a step portion 350 a that engages with an end surface of the common swash plate holder 180 that is on a far side from the center section 150B, and a center section-directed concave portion 355 forming a step 355 a that engages with an end surface of the center section 150B that is on a far side from the common swash plate holder 180, as the engagement concave portions.

Also, the inner surface of the sub-plate 170B is provided with a swash plate holder-directed concave portion 360 forming a step portion 360 a that engages with the end surface of the common swash plate holder 180 that is on the far side from the center section 150B, and a center section-directed concave portion 365 forming a step portion 365 a that engages with the end surface of the center section 150B that is on the far side from the common swash plate holder 180, as the engagement concave portions.

Providing such a configuration allows the main plate 160B and the sub-plate 170B to stabilize the supporting state of the HST preassembly.

Third Embodiment

A still another embodiment of the HST according to the present invention will be described below with reference to the accompanying drawings.

FIG. 18 illustrates a vertical cross-sectional view of an HST 100C according to the present embodiment in a state of being mounted on the transmission case 20, as viewed from the inside of the transmission case 20.

In the figure, the same components as those in the first and second embodiment described above are designated by the same reference numerals and the description thereof will be omitted as appropriate

The HST 100C according to the present embodiment is in common with the HST 100A according to the first embodiment in that the pump main body 115 and the motor main body 135 are respectively arranged on one side and the other side in the thickness direction of the center section 150C, but differs from the HST 100A in that the axial line positions of the pump main body 115 and the motor main body 135 are displaced from each other.

That is, in the HST 100C according to the present embodiment, the pump main body 115 is arranged on one side in the thickness direction of the center section 150C, while the motor main body 135 is arranged on the other side in the thickness direction of the center section 150C with the shaft line parallel to and at a different position from the shaft line of the pump main body 115.

Specifically, as illustrated in FIG. 18, the HST 100C includes: a center section 150C, a pump-side swash plate holder 125C, a motor-side swash plate holder 145C, a main plate 160C and a sub-plate 170C that hold or support the center section 150C, the pump-side swash plate holder 125C, and the motor-side swash plate holder 145C in a sandwiched manner in a state where the pump-side swash plate holder 125C and the motor-side swash plate holder 145C are respectively positioned on one side and the other side in the thickness direction of the center section 150B, the pump shaft 110 supported in a rotatable manner around the axial line by the center section 150C and the pump-side swash plate holder 125C, the pump main body 115 supported by the pump shaft 110 in a manner relatively non-rotatable around the axial line with respect to the pump shaft 110, the pump-side swash plate 120 having the rear surface supported by the pump-side swash plate holder 125C, the motor shaft 130 supported rotatably around the axial line by the center section 150C and the motor-side swash plate holder 145C in a manner to be parallel to the pump shaft 110 and to be different in the axial line position, the motor main body 135 supported by the motor shaft 130 in a manner relatively non-rotatable around the axial line with respect to the motor shaft 130, and the motor-side swash plate 140 having the rear surface supported by the motor-side swash plate holder 145B.

Similar to the main plate 160A in the first embodiment and the main plate 160B in the second embodiment, when viewed along the direction in which the main plate 160C and the sub-plate 170C face one another, the main plate 160C is provided with the extended region 162 extending farther outward in the planar direction than the installation space of the center section 150C, the pump-side swash plate holder 125C, and the motor-side swash plate holder 145C, and than the sub-plate 170C.

The inner surfaces of the main plate 160C and the sub-plate 170C are also provided with engagement concave portions into which the pump-side swash plate holder 125C, the center section 150C, and the motor-side swash plate holder 145C are engaged in a manner to prevent the HST preassembly from moving in the axial line direction.

The engagement concave portions for the center section 150C are so formed as to have step portions that engage with the end surfaces of the center section 150C on one side and the other side in the thickness direction.

The engagement concave portion for the pump-side swash plate holder 125C is so formed as to have a step portion that engages with an end surface of the pump-side swash plate holder 125C that is on a far side from the center section 150C.

The engagement concave portion for the motor-side swash plate holder 145C is so formed as to have a step portion that engages with an end surface of the motor-side swash plate holder 145C that is on a far side from the center section 150C.

DESCRIPTION OF THE REFERENCE NUMERALS

-   -   10A-10C transmission     -   20 transmission case     -   21 peripheral wall     -   22 opening     -   30 input-side transmission shaft     -   32 input-side transmission gear     -   35 output-side transmission shaft     -   37 output-side transmission gear     -   100A-100C HST     -   110 pump shaft     -   112 pump-side transmission gear     -   115 pump main body     -   120 pump-side swash plate     -   125A-125C pump-side swash plate holder     -   130 motor shaft     -   132 motor-side transmission gear     -   135 motor main body     -   140 motor-side swash plate     -   145A-145C motor-side swash plate holder     -   150A-150C center section     -   160A-160C main plate     -   162 extended region     -   165 center section-directed concave portion     -   166 pump-side concave portion     -   167 motor-side concave portion     -   170A-170C sub-plate     -   175 center section-directed concave portion     -   176 pump-side concave portion     -   177 motor-side concave portion     -   180 single common swash plate holder     -   200 hydraulic servo mechanism     -   205 connecting rod     -   210 pushing piston     -   215(1), 215(2) first and hydraulic oil chambers     -   220 switching spool     -   230 operating piston     -   235(1), 235(2) first and second operation oil chambers     -   250 operating valve     -   260 manual operating mechanism     -   350, 355, 360, 365 concave portion 

1. An HST comprising: a pump shaft; a pump main body supported by the pump shaft in a manner relatively non-rotatable around an axial line with respect to the pump shaft; a pump-side swash plate defining a capacity of the pump main body; a pump-side swash plate holder supporting a rear surface of the pump-side swash plate; a motor shaft; a motor main body supported by the motor shaft in a manner relatively non-rotatable around an axial line with respect to the motor shaft; a motor-side swash plate defining a capacity of the motor main body; a motor-side swash plate holder supporting a rear surface of the motor-side swash plate; a center section on which the pump main body and the motor main body directly or indirectly abut in a slidable manner around the respective axial lines and which is formed with oil paths fluidly connecting the pump main body and the motor main body; and a main plate and a sub-plate hold or support the center section, the pump-side swash plate holder and the motor-side swash plate holder in a sandwiched manner by inner surfaces of the main plate and the sub-plate that face each other, wherein the main plate is provided with an extended region that extends farther outward in a planar direction of the main plate than an installation space of the center section, the pump-side swash plate holder and the motor-side swash plate holder, and than the sub-plate as viewed along a direction in which the main plate and the sub-plate face each other.
 2. The HST according to claim 1, wherein the pump main body and the motor main body that are respectively arranged on one side and the other side in a thickness direction of the center section while being coaxially with each other.
 3. The HST according to claim 1 wherein the pump main body is arranged on one side in the thickness direction of the center section, and wherein the motor main body is arranged on the other side in the thickness direction of the center section with a shaft line of the motor main body being parallel to and displaced from a shaft line of the pump main body.
 4. The HST according to claim 2, wherein an inner surface of at least one of the main plate and the sub-plate is provided with a pump-side concave portion into which the pump-side swash plate holder is engaged and a motor-side concave portion into which the motor-side swash plate holder is engaged, wherein the pump-side concave portion and the motor-side concave portion are so configured as to prevent the pump-side swash plate holder and the motor-side swash plate holder from moving in a direction away from or a direction close to the center section with respect to the thickness direction of the center section.
 5. The HST according to claim 2, wherein an inner surface of at least one of the main plate and the sub-plate is provided with a center section-directed concave portion in which the center section is engaged in a manner to be immovable in the thickness direction of the center section.
 6. The HST according to claim 1, wherein the pump main body and the motor main body are arranged on one side in a thickness direction of the center section with their axial lines being parallel to each other.
 7. The HST according to claim 6, comprising a common swash plate holder integrally including the pump-side swash plate holder and the motor-side swash plate holder.
 8. The HST according to claim 7, wherein an inner surface of at least one of the main plate and the sub-plate is provided with an engagement concave portion into which at least one of the common swash plate and the center section so as to prevent an HST preassembly in which the center section, the pump shaft, the pump main body, the pump-side swash plate, the motor shaft, the motor main body, the motor-side swash plate and the common swash plate holder are assembled from moving in the axial line direction of the pump shaft.
 9. The HST according to claim 1, wherein at least one of the pump-side swash plate holder and the motor-side swash plate holder supports the rear surface of the corresponding swash plate in such a manner that the corresponding swash plate is swingable around a swing axial line, and wherein the main plate is provided with a hydraulic servo mechanism that swings a movable swash plate, which is supported in a swingable manner around the corresponding swing axial line among the pump-side swash plate and the motor-side swash plate, around the corresponding swing axial line.
 10. The HST according to claim 9, wherein the hydraulic servo mechanism includes a pushing piston that is housed in the main plate in a manner to be reciprocally movable in a pushing direction and is operatively connected to the movable swash plate via a connecting rod so that the movable swash plate swings around the swing axial line in accordance with a movement of the pushing piston along the pushing direction, first and second hydraulic oil chambers formed in the main plate in such a manner that pressure oil supplied into the first and second hydraulic oil chambers push the pushing piston to one side and the other side in the pushing direction, respectively, a switching spool that switches supply and discharge of pressure oil to and from the first and second hydraulic oil chambers in accordance with a position in a switching direction, an operating piston that is housed in the main plate in a manner to be reciprocally movable in an operating direction parallel to the switching direction and is operatively connected to the switching spool via a connection pin, first and second operation oil chambers formed in the main plate in such a manner that pressure oil supplied into the first and second operation oil chambers push the operating piston to one side and the other side in the operating direction, and an operating valve that switches supply and discharge of pressure oil to and from the first and second operation oil chambers, and wherein the main plate is provided with a manual operating mechanism capable of manually changing the position of the switching spool in the switching direction.
 11. A transmission that speed-changes rotational power operatively input from a drive source, the transmission comprising: a transmission case; an input-side transmission shaft that is operatively connected to the drive source and is supported by the transmission case in a rotatable manner around an axial line; an input-side transmission gear supported by the input-side transmission shaft in a manner relatively non-rotatable around an axial line with respect to the input-side transmission shaft within the transmission case; an output-side transmission shaft supported by the transmission case in a rotatable manner around an axial line; an output-side transmission gear supported by the output-side transmission shaft in a manner relatively non-rotatable manner around an axial line with respect to the output-side transmission shaft within the transmission case; and an HST, wherein the HST includes a pump shaft, a pump main body supported by the pump shaft in a manner relatively non-rotatable around an axial line with respect to the pump shaft, a pump-side swash plate defining a capacity of the pump main body, a pump-side swash plate holder that supports a rear surface of the pump-side swash plate and is formed with a through hole through which the pump shaft is passed, a pump-side transmission gear supported by a portion of the pump shaft that extends from a portion passing through the pump-side swash plate holder in a direction away from the pump main body in such a manner that the pump-side transmission gear is relatively non-rotatable around the axial line with respect to the pump shaft, a motor shaft, a motor main body supported by the motor shaft in a manner relatively non-rotatable around an axial line with respect to the motor shaft, a motor-side swash plate defining a capacity of the motor main body, a motor-side swash plate holder that supports a rear surface of the motor-side swash plate and is formed with a through hole through which the motor shaft is passed, a motor-side transmission gear supported by a portion of the motor shaft that extends from a portion passing through the motor-side swash plate holder in a direction away from the motor main body in such a manner that the motor-side transmission gear is relatively non-rotatable around the axial line with respect to the motor shaft, a center section that is formed with oil paths fluidly connecting the pump main body and the motor main body, and a main plate and a sub-plate hold or support the center section, the pump-side swash plate holder and the motor-side swash plate holder in a sandwiched manner by inner surfaces of the main plate and the sub-plate that face each other, wherein the transmission case has a peripheral wall and an opening formed in the peripheral wall, wherein the opening is so sized as to allow, in an assembled state of the HST, insertion of components other than the main plate of the HST, wherein the main plate is detachably connected to an outer surface of the peripheral wall of the transmission case so that the components of the HST other than the main plate is housed within the transmission case via the opening, and wherein the pump-side transmission gear and the motor-side transmission gear mesh with the input-side transmission gear and the output-side transmission gear, respectively, in accordance with connection of the main plate to the outer surface of the peripheral wall of the transmission case.
 12. The transmission according to claim 11, wherein the main plate is formed with a supply oil path having one end portion opened to an outer surface to form an inlet port for receiving charge oil of operation oil of the HST, and wherein a part of oil that is supplied into the supply oil path is introduced into an axial line hole of the pump shaft via the pump-side swash plate holder and an axial line hole of the motor shaft via the motor-side swash plate holder, and then is supplied to respective sites to be lubricated via the axial line holes. 